Hair colouring is a common practice for ages. Oxidative colouration has been widely used for achieving durable, brilliant hair colour. Direct dyes, either of cationic or of anionic character, have also found their applications for colouring hair.
In practice, number of difficulties are observed when colouring human hair. One of them is variation in resulting hair colour with physical status of the hair. Good colouring performance is usually obtained with healthy, natural hair, whereas the colouring performance is not always found to be satisfactory in cases of damaged, chemically processed hair and especially with those of bleached hair. The reason underlying in performance difference may be that, penetration of the dyestuffs is varied with the degree of damages previously caused to the hair fibre. In daily hair colouring practice, this results in uneven colourations, colours lacking brilliance and durability.